This invention relates to a composition and method to remove major contaminants that accumulate as fats and oils are used to fry foods such as potato chips, chicken, french fries, etc. In particular, my invention provides for using a blend of synthetic amorphous silica gel and alumina to rejuvenate cooking oils used in the frying of various foods. The term oil(s) or frying oil(s) as used herein include materials of vegetable and animal origin. Examples include oils and fats derived from soybeans, cottonseeds, peanuts, olives, palm seeds, canola/rapeseeds and corn as well as beef fat or tallow. Frying oils are often combinations of these materials.
Frying oils decompose over time and use due to the formation and acquisition of various contaminants during cooking. Soaps, polar compounds, polymers, free fatty acids (FFA), color bodies and trace metals are the major contaminants which contribute to oil degradation through increased instability. The cooking process and the accumulation of these contaminants also result in a visibly darker color to the oil which can be displeasing in appearance. The longer the oil is used without treatment, the higher the levels of contaminants and the darker the color becomes. See Table 1, which summarizes data from my experiments.
TABLE 1 ______________________________________ Color FFA Stability Polar Oil Cooking Red/ Wt (Peroxide Soaps Compounds Type Time Yellow % Value) ppm Wt % ______________________________________ Fresh -- .2/.6 .01 2.5 2 2.4 Peanut 3 days 4.4/40 .05 2.8 -- -- Peanut 7 days 22/59 .53 10.4 -- -- Peanut 1 days 1.7/-- .05 -- 40 14.0 ______________________________________
The above results also demonstrate a higher peroxide value (PV), which is a known indicator for oil stability. The higher the PV, the greater the instability of the oil; therefore, the oil will oxidize and become rancid more quickly.
Each of these contaminants can contribute different problems to the frying oil and to the food being fried therein. FFA can react with the trace metals found in oil to form soaps. The formation of soaps can result in higher oil absorption by the food being fried. This can result in a greasier product, as well as an overcooked or harder finished food product, internally as well as on the surface. The presence of soaps also causes excessive foaming of the oil. Such foaming, if unchecked, is known to be a safety hazard for the operators of the frying equipment.
Polar compounds can contribute to off flavors in the product, as well as increased oxidation of the oil. Trace metals such as Mg, P, Cu and Fe can react with oxygen from the air to catalyze the oxidation process resulting in a high PV of the oil. This causes the oil to become rancid in a much shorter time. Products that contain oil with a high PV value degrade more quickly when stored.
FFA, along with polar compounds, can also result in the formation of film or coke deposits along the side of frying equipment.
Compositions and methods have been suggested for removing the many impurities from used oils. None of these have specifically addressed the removal of all the contaminants that degrade the oil, but have singularly attacked the contaminants believed to be most troublesome in a specific system. For example, calcium and magnesium silicates are currently marketed as active filter aids specifically for FFA reduction. These products have been shown to reduce FFA, but at the expense of forming soaps or releasing calcium or magnesium metals into the frying medium. See Table 2, which summarizes data from my experiments that support this finding.
TABLE 2 ______________________________________ FFA Metals Soaps Oil Treatment Wt % ppm ppm ______________________________________ Tallow/CSO Untreated 1.52 &lt;10 41.0 Tallow/CSO Ca Silicate 1.02 120 150.0 ______________________________________
A method and composition for treating used cooking oil by mixing said oil at a temperature of 300.degree. F. with a composition of a porous carrier, water, and food compatible acid is disclosed in U.S. Pat. No. 4,330,564. The addition of the acid is apparently directed to counteracting soap formation.
Another method of treating cooking oil in which the cooking oil is contacted with food-compatible acid, followed by separation of the oil from the acid before reuse of the oil is disclosed in U.S. Pat. No. 3,947,602. The addition of the acid is apparently directed to counteracting soap formation.
U.S. Pat. No. 3,232,390 discloses a method of reducing the FFA content and increasing the smoke point of used cooking oil by mixing said oil with an adsorbent and then separating said adsorbent after about 3 to 15 minutes. The adsorbent is selected from a group consisting of alkaline earth oxides and carbonates. U.S. Pat. No. 4,681,768 discloses a method of reducing FFA content of used cooking oil wherein the oil is contacted with magnesium silicate of certain properties. The patent discloses that the magnesium silicate is hydrated.
U.S. Pat. Nos. 4,629,588 and 4,734,226 disclose the use of various silicas and acid-treated silicas in the "refining" of glyceride oils for removal of trace contaminants, specifically trace metals and phospholipids in the refining process. These patents, like those cited before, are narrow of scope and do not discuss the other contaminants found in used cooking oils.
U.S. Pat. No. 4,735,815 discloses a method of reducing FFA with a composition of activated clay or magnesium silicate and alumina derived from a gel, said composition containing 15% to 75% by weight of alumina. Color is also reduced, and extended service life is indicated.
All of these patents are directed to various aspects of refining or reclaiming various cooking or frying oils through removal of specific contaminants. None of the patents are directed to removing levels of all of the key contaminants that degrade frying oils. It is an object of this invention to reduce the level of all contaminants generally found in used cooking oils, specifically FFA, polar compounds, and color bodies, as well as the reduction of soaps and trace metals (Ca, Mg, P, Cu, Fe), by sorption on the surface of the adsorbent composition. It is a further objective to improve the stability of the oil by lowering the PV of the oil. It is another object of my invention to reduce foaming of used oil. It is a further objective to provide a composition of material that can remove or reduce all of the contaminants at the same time in a single process.